1. Field of the Invention
The present invention relates to a process cartridge and an electrophotographic apparatus having a specific electrophotographic photosensitive member and a specific charging member.
2. Description of the Related Art
Charging means, which have been conventionally used for electrophotographic apparatuses, such as copying machines and laser beam printers, use corona charging and direct contact charging of a photosensitive member surface using a roller or a brush. Corona charging has several problems, such as the generation of ozone due to atmospheric discharge, high electrical facility costs due to the use of a high-voltage power source, and contamination of wiring due to corona discharge products. A proposed charging means for solving such problems is a contact charging means in which a charging member, such as a roller or brush, is brought into direct contact with a photosensitive layer surface and a voltage is applied to the charging member to charge the photosensitive member, as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 7-114249 and 7-98534.
An electrophotographic photosensitive member generally includes a substrate and a photosensitive layer provided thereon for forming a latent image by charge or exposure. Fundamental requirements for the electrophotographic photosensitive member are sensitivity, and electrical and optical characteristics responsible for an applied electrophotographic process. Another requirement is environmental stability so that the electrophotographic photosensitive member sufficiently demonstrates the above characteristics in any environment from low temperature and low humidity to high temperature and high humidity.
Typical image defects include lines, black dots in blanks, white dots in black backgrounds, and fogging in blanks. Furthermore, fringes will occur due to the surface shape of the substrate and the uneven thickness of the photosensitive member in a digital copying machine or a laser beam printer using a light source having a single wavelength for exposure. Thus, countermeasures for avoiding the image defects are required in the production of the photosensitive members.
Major factors causing the image defects include foreign materials on the substrate, chemical impurities, such as contaminant elements contained in aluminum, and flaws such as flashes and pinholes on the substrate surfaces. In contact charging means, these chemical impurities and mechanical defects readily cause electrical leakage, and unsuccessful charge and image defects are significantly noticeable compared to corona charging.
A proposed configuration to prevent electrical leakage provides an intermediate layer, composed of an organic polymer, having an electrical blocking effect or containing metal oxide dispersed therein. Japanese Patent Application Laid-Open No. 5-34964 discloses the providing of an aluminum oxide layer by anodic oxidation of an aluminum substrate surface. Other surface oxidation techniques for aluminum substrates are, for example, the formation of chromate films, as disclosed in Japanese Patent Application Laid-Open Nos. 58-12733 and 57-62056; the formation of boehmite films, as disclosed in Japanese Patent Application Laid-Open Nos. 58-14841 and 64-29852; and the formation of oxide films by forced oxidation at high temperatures, as disclosed in Japanese Patent Application Laid-Open No. 57-29051.
In anodic oxidation, however, the thickness of the oxide film on the substrate must be at least 5 to 6 xcexcm in order to form a uniform film, although this method can solve the above problems. Such a large thickness causes an increased residual potential and decreased sensitivity, in addition to increased process and material costs.
In the chromation process, it is significantly difficult to dispose the waste solution containing chromium in an environmentally safe way, in spite of the relatively satisfactory characteristics of the substrate.
In the boehmite treatment, the crystalline state of the resulting surface is not necessarily suitable for a substrate for electrophotographic photosensitive members, and thus satisfactory images are not obtainable.
Accordingly, it is an object of the present invention to provide a process cartridge and an electrophotographic apparatus which can prevent the formation of image defects in any environment, from low temperature and low humidity to high temperature and high humidity, even when a contact charging means is used as a charging means.
As a result of investigations for solving the above-discussed problems, a significantly effective means to prevent image defects in a contact charging means was discovered by using an electrophotographic photosensitive member which has an insoluble film having a specific composition provided on a substrate. The film is formed by a specific chemical treatment of the surface of the aluminum substrate used for the electrophotographic photosensitive member, that is, by a chemical reaction of the substrate with an acidic aqueous solution containing a specific metallic element without using electrical force.
According to a first aspect of the present invention, a process cartridge includes an electrophotographic photosensitive member and a charging member for charging the electrophotographic photosensitive member by the application of a voltage, the charging member being in contact with the electrophotographic photosensitive member, the electrophotographic photosensitive member and the charging member being integrally supported and being mountable to and detachable from an electrophotographic apparatus body. The electrophotographic photosensitive member includes an aluminum substrate and a photosensitive layer provided thereon, the outermost surface of the substrate containing the elements of aluminum, oxygen, and at least one of titanium and zirconium.
According to a second aspect of the present invention, an electrophotographic apparatus includes an electrophotographic photosensitive member, a charging member for charging the electrophotographic photosensitive member by the application of a voltage, the charging member being in contact with the electrophotographic photosensitive member, an exposure means, a developing means, and a transfer means. The electrophotographic photosensitive member includes an aluminum substrate and a photosensitive layer provided thereon, the outermost surface of the substrate containing the elements of aluminum, oxygen, and at least one of titanium and zirconium.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.